Re: [PATCH v1] vdpa/mlx5: Restore the hardware used index after change map

[Jason Wang]

On 2021/2/6 上午7:07, Si-Wei Liu wrote:
> On 2/3/2021 11:36 PM, Eli Cohen wrote:
> > When a change of memory map occurs, the hardware resources are destroyed
> > and then re-created again with the new memory map. In such case, we need
> > to restore the hardware available and used indices. The driver failed to
> > restore the used index which is added here.
> >
> > Also, since the driver also fails to reset the available and used
> > indices upon device reset, fix this here to avoid regression caused by
> > the fact that used index may not be zero upon device reset.
> >
> > Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 
> > devices")
> > Signed-off-by: Eli Cohen <elic@xxxxxxxxxx>
> > ---
> > v0 -> v1:
> > Clear indices upon device reset
> >
> >   drivers/vdpa/mlx5/net/mlx5_vnet.c | 18 ++++++++++++++++++
> >   1 file changed, 18 insertions(+)
> >
> > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c 
> > b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > index 88dde3455bfd..b5fe6d2ad22f 100644
> > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > @@ -87,6 +87,7 @@ struct mlx5_vq_restore_info {
> >       u64 device_addr;
> >       u64 driver_addr;
> >       u16 avail_index;
> > +    u16 used_index;
> >       bool ready;
> >       struct vdpa_callback cb;
> >       bool restore;
> > @@ -121,6 +122,7 @@ struct mlx5_vdpa_virtqueue {
> >       u32 virtq_id;
> >       struct mlx5_vdpa_net *ndev;
> >       u16 avail_idx;
> > +    u16 used_idx;
> >       int fw_state;
> >         /* keep last in the struct */
> > @@ -804,6 +806,7 @@ static int create_virtqueue(struct mlx5_vdpa_net 
> > *ndev, struct mlx5_vdpa_virtque
> >         obj_context = MLX5_ADDR_OF(create_virtio_net_q_in, in, 
> > obj_context);
> >       MLX5_SET(virtio_net_q_object, obj_context, hw_available_index, 
> > mvq->avail_idx);
> > +    MLX5_SET(virtio_net_q_object, obj_context, hw_used_index, 
> > mvq->used_idx);
> >       MLX5_SET(virtio_net_q_object, obj_context, 
> > queue_feature_bit_mask_12_3,
> >            get_features_12_3(ndev->mvdev.actual_features));
> >       vq_ctx = MLX5_ADDR_OF(virtio_net_q_object, obj_context, 
> > virtio_q_context);
> > @@ -1022,6 +1025,7 @@ static int connect_qps(struct mlx5_vdpa_net 
> > *ndev, struct mlx5_vdpa_virtqueue *m
> >   struct mlx5_virtq_attr {
> >       u8 state;
> >       u16 available_index;
> > +    u16 used_index;
> >   };
> >     static int query_virtqueue(struct mlx5_vdpa_net *ndev, struct 
> > mlx5_vdpa_virtqueue *mvq,
> > @@ -1052,6 +1056,7 @@ static int query_virtqueue(struct mlx5_vdpa_net 
> > *ndev, struct mlx5_vdpa_virtqueu
> >       memset(attr, 0, sizeof(*attr));
> >       attr->state = MLX5_GET(virtio_net_q_object, obj_context, state);
> >       attr->available_index = MLX5_GET(virtio_net_q_object, 
> > obj_context, hw_available_index);
> > +    attr->used_index = MLX5_GET(virtio_net_q_object, obj_context, 
> > hw_used_index);
> >       kfree(out);
> >       return 0;
> >   @@ -1535,6 +1540,16 @@ static void teardown_virtqueues(struct 
> > mlx5_vdpa_net *ndev)
> >       }
> >   }
> >   +static void clear_virtqueues(struct mlx5_vdpa_net *ndev)
> > +{
> > +    int i;
> > +
> > +    for (i = ndev->mvdev.max_vqs - 1; i >= 0; i--) {
> > +        ndev->vqs[i].avail_idx = 0;
> > +        ndev->vqs[i].used_idx = 0;
> > +    }
> > +}
> > +
> >   /* TODO: cross-endian support */
> >   static inline bool mlx5_vdpa_is_little_endian(struct mlx5_vdpa_dev 
> > *mvdev)
> >   {
> > @@ -1610,6 +1625,7 @@ static int save_channel_info(struct 
> > mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqu
> >           return err;
> >         ri->avail_index = attr.available_index;
> > +    ri->used_index = attr.used_index;
> >       ri->ready = mvq->ready;
> >       ri->num_ent = mvq->num_ent;
> >       ri->desc_addr = mvq->desc_addr;
> > @@ -1654,6 +1670,7 @@ static void restore_channels_info(struct 
> > mlx5_vdpa_net *ndev)
> >               continue;
> >             mvq->avail_idx = ri->avail_index;
> > +        mvq->used_idx = ri->used_index;
> >           mvq->ready = ri->ready;
> >           mvq->num_ent = ri->num_ent;
> >           mvq->desc_addr = ri->desc_addr;
> > @@ -1768,6 +1785,7 @@ static void mlx5_vdpa_set_status(struct 
> > vdpa_device *vdev, u8 status)
> >       if (!status) {
> >           mlx5_vdpa_info(mvdev, "performing device reset\n");
> >           teardown_driver(ndev);
> > +        clear_virtqueues(ndev);
> The clearing looks fine at the first glance, as it aligns with the 
> other state cleanups floating around at the same place. However, the 
> thing is get_vq_state() is supposed to be called right after to get 
> sync'ed with the latest internal avail_index from device while vq is 
> stopped. The index was saved in the driver software at vq suspension, 
> but before the virtq object is destroyed. We shouldn't clear the 
> avail_index too early.


Good point.

There's a limitation on the virtio spec and vDPA framework that we can 
not simply differ device suspending from device reset.

Need to think about that. I suggest a new state in [1], the issue is 
that people doesn't like the asynchronous API that it introduces.


> Possibly it can be postponed to where VIRTIO_CONFIG_S_DRIVER_OK gets 
> set again, i.e. right before the setup_driver() in 
> mlx5_vdpa_set_status()?


Looks like a good workaround.

Thanks


> -Siwei


[1] 
https://lists.oasis-open.org/archives/virtio-comment/202012/msg00029.html


> > mlx5_vdpa_destroy_mr(&ndev->mvdev);
> >           ndev->mvdev.status = 0;
> >           ndev->mvdev.mlx_features = 0;